Magnetorheological fluid composition and a process for preparation thereof

ABSTRACT

The present invention relates to a magnetorheological fluid composition and a process for preparing the same, which has excellent magnetorheological properties. The fluid composition exhibits change in rheological characteristics in the presence of an external magnetic field. Further, the magnetorheological characteristics of the fluid composition can be optimised for the improved magnetic sensitivity to external magnetic field and negligible magnetic retentivity after removal of the external magnetic field. The sensitivity of the fluid to external magnetic field can be varied by varying the pure iron content of the magnetic sensitive particles composition while, the magnetic retentivity of the fluid (after removal of external magnetic field) can be varied by varying the ferrite alloy content of the same. The fluid composition utilises a magnetic sensitive particles stabiliser or surfactant, which is synthesised from the carrier fluid used in the fluid composition. The fluid composition, prepared according to this process, does not suffer from the rapid settling of the magnetic particles as it utilises a carrier fluid based surfactant, which improves the homogeneity of the fluid composition.

FIELD OF INVENTION

This invention relates to magnetorheological fluid composition and aprocess for preparation thereof.

PRIOR ART

A magnetorheological fluid comprises a uniform dispersion of magneticresponsive particles in a fluid carrier medium dispersed with the aid ofsurfactants. These fluids change their flow or Theologicalcharacteristics in a very short time under the influence of an externalmagnetic field and these fluids find applications in electromechanicalactuators, wherein these fluids act as an interface between a sensingdevice and a required mechanical output device. In case of automotiveapplications, these fluids are utilised in shock absorbers, vibrationdampers etc. These fluids also find applications in devices such asrotary seals, bearings and other related devices. However, thesemagnetorheological fluids must have a high degree of stability in orderto be applicable.

Generally, a stable magnetic fluid in a high magnetic field gradientrequires small sits magnetic responsive particles having diameter lessthan 1000 A°. These magnetic responsive particles are coated with layersof surfactants. Each particle has a constant magnetic dipole momentproportional to its size that can align with the applied externalmagnetic field. Surfactants are employed to enhance the homogeneity ofthe resultant magnetorheological fluid composition In the absence ofsurfactant coatings, the magnetic responsive particles have tendency toquickly settle inside the carrier fluid due to large difference in thedensity of such particles and the carrier fluid The magnetic responsiveparticles, employed, could be iron oxide, iron, iron carbide, low carbonsteel or alloys of zinc, nickel, manganese or cobalt etc. Similarly, thecarrier fluids could be hydrocarbon oils, paraffin, mineral oils,polyester and phosphate esters etc. Additionally, certain additives likeantioxidants or anti-wear agents are also employed in the fluidcompositions. The carrier fluid should be preferably non-volatile,non-inflammable, non-toxic and stable over a wide range of operatingtemperature.

In the absence of magnetic field, the magnetorheological fluid has ameasurable viscosity, which depends upon several parameters like shearrate, temperature etc. however, in presence of an external magneticfield, the viscosity of the fluid increases to a very high value as thesuspended particles align themselves resulting in rapid physical gellingof the fluid. The viscosity changes closely follow the bingham plasticsbehavior, wherein the yield stress in a function of the strength of theapplied magnetic field. The magnetic field force induces alignment ofthe otherwise random dispersion of magnetic sensitive particles of thefluid into chain like structures offering increased resistance to flow,which is responsible for the build up of “yield strength”. On removal ofmagnetic field the structure crumbles and fluidity of the materialreturns to is original value. An ideal magnetorheological fluidcomposition should be highly sensitive to the applied magnetic field butat the same time it should return back to its original condition offluidity as soon as the external magnetic field is removed.

The magnetorheological fluid compositions and their applications arewell known to the prior art. However, the magnetorheological fluidcompositions, know in the prior art, suffer from followingdisadvantages.

Main disadvantage of the known magnetorheological fluid compositions isthat these magnetorheological fluid compositions are not optimised fordesirable combination of contradicting properties viz improved magneticsensitivity in the presence of external magnetic field and leastmagnetic retentivity after removal of the external magnetic field.

Another disadvantage of the know magnetorheological fluid compositionsis that these fluids suffer from rapid settling of magnetic responsiveparticles as these fluids employ surfactants generically different fromcarrier fluids employed and thereby adversely affecting the settlingresistance of the magnetic responsive particles due to their gravitydifference with the carrier fluid.

Still another disadvantage of the known magnetorheological fluidcompositions is that these fluid compositions generally employhydrocarbon and mineral oils as carrier fluids, which are obtainedthrough complex processes.

Yet further disadvantage of the known magnetorheological fluidcompositions is that these fluid compositions employ carrier fluidswhich are not available from renewable sources.

Still further disadvantage of the known magnetorheological fluidcompositions is that the process for preparing these fluid compositionsis complex

OBJECTS OF THE INVENTION

Primary object of the invention is to provide a magnetorheological fluidcomposition and a process for preparing the same wherein themagnetorheological fluid has excellent magnetorheological properties.

Another object of the invention is to provide a magnetorheological fluidcomposition and a process for preparing the same wherein the Brookfieldviscosity of the magnetorheological fluid can be changed continuouslyover a wide range, typically from 500 CP to 120000 CP and beyond byvarying the strength of magnetic field.

Yet another object of the invention is to provide a magnetorheologicalfluid composition and a process for preparing the same wherein themagnetorheological fluid has optimised combination of high magneticsensitivity in the presence of external magnetic field and low magneticretentivity after removal of the external magnetic field.

Still another object of the invention is to provide a magnetorheologicalfluid composition and a process for preparing the same wherein thesensitivity of the magnetorheological fluid to the external field can bevaried by varying the weight percentage of pure iron particles contentand magnetic retentivity can be varied by varying the weight percentageof ferrite alloys content.

Yet another object of the invention is to provide a magnetorheologicalfluid composition and a process for preparing the same, wherein themagnetorheological fluid does not suffer from the rapid settling of themagnetic responsive particles as it utilises a carrier fluid basedsurfactant thereby improving the homogeneity of the fluid composition.

Still another object of the invention is to provide a magnetorheologicalfluid composition and a process for the preparing the same wherein themagnetorheological fluid utilises a vegetable oil extracted from anagro-seed as a carrier fluid.

Still further object of the invention is to provide a magnetorheologicalfluid composition and a process for the preparation of the same whereinthe magnetorheological fluid does not utilise additives likeorganomolybdenum, thiophosphorus, thiocarbamate, alkyl amines etc.

Yet further object of the invention is to provide a magnetorheologicalfluid composition and a process for preparing the same wherein themagnetorheological fluid is insensitive to the normal level ofcontamination.

Still further object of the invention is to provide a magnetorheologicalfluid composition and a process for preparing the same wherein themagnetorheological fluid has low hysteresis characteristics.

Yet further object of the invention is to provide a magnetorheologicalfluid composition and a process for preparing the same wherein themagnetorheological fluid can be used for wide temperature range from−10° C. to +80° C.

Yet another object of the invention is to provide a magnetorheologicalfluid composition and a process for preparing the same wherein themagnetorheological fluid utilises a carrier fluid which is easilyavailable.

Still further object of the invention is to provide a magnetorheologicalfluid composition and a process for preparing the same wherein themagnetorheological fluid utilises a carrier fluid which depends uponrenewable source of supply.

Yet further object of the invention is to provide a magnetorheologicalfluid composition and a process for preparing the same wherein themagnetorheological fluid utilises a carrier fluid which is eco-friendly.

Still further object of the invention is to provide a magnetorheologicalfluid composition and a process for preparing the same wherein themagnetorheological fluid has improved stability.

Yet further object of the invention is to provide a magnetorheologicalfluid composition and a process for preparing the same wherein theprocess of preparation is very simple.

Still another object of the invention is to provide a magnetorheologicalfluid composition and a process for preparing the same wherein theviscosity of the magnetorheological fluid can be continuously changedwith the application of the magnetic field.

Still further object of the invention is to provide a magnetorheologicalfluid and a process for preparing the same wherein themagnetorheological fluid can be utilised for marking controllabledevices and adaptive structures, such as dampers, mounts etc and rotarydevices like clutches, brakes, valves etc.

DESCRIPTION OF THE INVENTION

According to this invention there is provided the proposedmagnetorheological fluid utilises castor oil, a derivative of vegetableoil extracted from agro-seed as a carrier fluid This carrier fluid i.e.castor oil is cheaper, easily available, eco-friendly, biocompatible andhas renewable source of supply Further, this carrier fluid does notrequire additives like thiophosphorus, thiocarbamate and amines. Themagnetorheological fluid composition comprises magnetic responsiveparticles such as iron and its alloys, all know iron oxides, ironnitride, iron carbide, carbonyl. The proposed process for preparation ofdie magnetorheological fluid is simpler and does not need complexmachinery. The Brookfield viscosity of the magnetic fluid can becontinuously varied over a wide range from 500 CP to 120000 CP andbeyond under the influence of external magnetic field. However,viscosity of the magnetorheological fluid composition depends on theviscosity of the cancer fluid employed therein.

DETAILED DESCRIPTION OF THE PROCESS

According to the present invention, the process for the preparation ofthe magnetorheological fluid composition comprises of following steps.

(i) Preparation of Magnetic Sensitive Particles

-   -   80 to 95% by weight of commercially available high purity iron        particles such as carbonyl iron and 5 to 20% by weight of        commercially available ferrite alloys such as nickel-Zinc        ferrite or manganese zinc ferrite are dry blended using a powder        blender.        (i) Preparation of Magnetic Sensitive Particles Stabiliser        (Surfactant)

90 to 98% by weight of castor oil of commercial purity (viscosity about700-800 Cps) and 1 to 5% by weight of con. Sulphuric acid (assay 98%) ismixed by pouring sulphuric acid to the castor oil in a container, dropwise under continuous stirring. The temperature is maintained between 25to 30° C. using a water bath. The mix is further allowed to react fortwo hours with the temperature maintained between 25-30° C. Next, 1 to5% by weight of 20% aqueous solution of potassium hydroxide (potassiumhydroxide pellets≧85% purity, dissolved in distilled water) is addeddrop wise to this mix under continuous stirring with temperaturemaintained between 25 to 30° C. This mix is further allowed to react fortwo more hours at the same temperature, The magnetic sensitive particlestabiliser, thus obtained, is finally washed with distilled water tillthe water pH becomes neutral.

(ii) Coating of Magnetic Sensitive Particles Obtained from step (i) withthe Magnetic Sensitive Particles Stabiliser Obtained from Step (ii)

-   -   90 to 90% by weight of the magnetic sensitive particle, obtained        through step (i), is mixed with 1 to 10% of particle stabiliser,        obtained through step (ii) using a laboratory kneader. However,        before mixing, the magnetic sensitive particle drop wise to the        magnetic sensitive particles and mixed in a kneader. The mix,        thus obtained is allowed to mature for 24 hours at room        temperature.        (ii) Synthesis of Magnetorheological Fluid Composition

80 to 90% by weight of modified magnetic sensitive particles, obtainedthrough step (iii), are mixed with 10 to 20% by weight of commerciallyavailable low viscosity castor oil. Before mixing, the castor oil ispreheated to about 60-70° C. in a container and the modified magneticsensitive particles are added to it in a gradual fashion.

Once these particles are added to the oil, the mix is homogenised usinga high speed mixer in different stages. In the beginning, the mixingspeed of the mixer is increased from about 500 to 1000 rpm within first10 minutes of mixing and mixing is continued for about 1 hour.Subsequently, the homogenised mixed is cooled to room temperature. Inthe next stage, the mix is further agitated at a high rpm of 2000 to3000 for about 3 to 5 minutes and is allowed to cool to the roomtemperature. The above agitation at 3000 rpm is repeated once again toobtain the final product i.e.

The invention will now be illustrated with working examples, which aretypical examples to illustrate the working of the invention and are notintended to be taken restrictively to imply any limitation on the scopeof the present invention.

WORKING EXAMPLE-I

76.50 gm of high purity iron powder and 8.50 gm of nickel-zinc ferriteare dry blended in a powder blender. The magnetic sensitive particles,prepared in this manner, are stored separately for subsequentmodification with stabiliser. Next, 2.40 gm of castor oil of commercialpurity is mixed with 0.050 gm of concentrated sulfuric acid in acontainer while maintaining the temperature to 30° C. using a waterbath. Further, this mix is allowed to react for 2 hours at the sametemperature. In the next step, 0.050 gm of potassium hydroxide isdissolved in 2.50 ml distilled water in a container. This aqueoussolution of potassium hydroxide is added to the mix prepared in earlierstep drop wise under continuous stirring while maintaining thetemperature to the same level. This entire mix is further allowed toreact for two more hours. This mix is finally washed with distilledwater till the pH of the water becomes neutral. This product is utilisedto modify the magnetic sensitive particles using a laboratory kneader.The resulting modified magnetic sensitive particles are allowed tomature for 24 hours. Next, 12.50 gm of mono ester derivative ofcommercially available low viscosity castor oil is taken in a containerand heated to 70° C. The coated magnetic sensitive particles, obtainedfrom above step, are added to the hot castor oil and is mixed using ahigh speed mixer. The mixing speed is increased from 500 rpm to 1000 rpmand mixture is allowed to cool down to room temperature. The mixture isfurther agitated at high speed of 3000 rpm for 3-5 minutes andsubsequently, it is allowed to cool down to the room temperature. Theabove homogenisation cycle is again repeated to obtain 100 gmmagnetorheological fluid.

WORKING EXAMPLE-II

73.0 gm of high purity iron powder and 9.0 gm of manganese-zinc ferriteare dry blended in a powder blender. Next 4.40 gm of castor oil ofcommercial purity is mixed with 0.050 gm of concentrated sulfuric acidin a container while maintaining the temperature to 30° C. using a waterbath. Further, this mix is allowed to react for 2 hours at the sametemperature. In the next step, 0.050 gm of potassium hydroxide isdissolved in 2.50 ml distilled water in a container. The above aqueoussolution of potassium hydroxide is add to mix prepared in earlier stepdrop wise under continuous stirring while maintaining the temperature tothe same level. The entire mix is further allowed to react for two morehours. This mix is washed with distilled water till the pH of the waterbecomes neutral. This product is utilised to wet the dry blended powderusing a laboratory kneader. The resulting mix is allowed to mature for24 hours. Next, 13.50 gm of commercially available castor oil is takenin a container and heated at 70° C. The mix is added to the hot castoroil and is thoroughly mix using a high-speed mixer. The mixing speed isincreased from 500 rpm to 1000 and mixture is allowed to cool down toroom temperature. The mixture is further agitated at high speed of 3000rpm for 5 minutes and subsequently, it is allowed to cool down to theroom temperature. The above homogenising cycle is again repeated toobtain 100 gm magnetorheological fluid.

It is to be understood that the process of the present invention issusceptible to adaptations, changes and modifications by those skilledin the art. Such adaptations, changes and modifications are intended tobe within the scope of the present invention, which is further set forthwith the following claims.

1. A magnetorheological fluid composition comprising: (a) 10-20% byweight of castor oil as a carrier fluid; and (b) 80-90% by weight ofmagnetic sensitive particles coated with magnetic sensitive particlesstabiliser and dispersed in the said carrier fluid wherein the saidmagnetic sensitive particles stabiliser is synthesised from the saidcarrier fluid and comprises 90-98% by weight of said carrier fluid, 1-5%by weight of conc. sulphuric acid (assay 98%) and 1-5% by weight ofaqueous solution of potassium hydroxide.
 2. A magnetorheological fluidcomposition as claimed in claim 1, wherein the said magnetic sensitiveparticles comprises 80-95% by weight of high purity iron particles and5-20% by weight of ferrite alloys.
 3. A process for the preparation ofmagnetorheological fluid composition having castor oil as a carrierfluid and magnetic sensitive particles coated with the magneticsensitive particles stabiliser the said process comprising the steps of:(i) preparing magnetic sensitive particles by dry blending 80-95% byweight of high purity ion particles such as carbonyl iron and 5-20% byweight of ferrite alloys; (ii) preparing magnetic sensitive particlesstabiliser comprising the steps of adding 1-5% by weight of concentratedsulphuric acid drop wise to 90-98% by weight of the said carrier fluidin a container under continuous stirring and allowing them to react forabout 2 hours with temperature maintained at about 25-30° C. adding 1-5%by weight of an aqueous solution of potassium hydroxide to the reactionproduct of sulphuric acid and carrier fluid under continuous stirringallowing the entire mix to react for about two hours with thetemperature maintained at about 25-30° C., washing the magneticsensitive particles stabiliser; (iii) coating the said magneticsensitive particles obtained from step (i) with the said magneticparticles stabiliser prepared in step (ii) by heating 1-10% of the saidparticle stabiliser to 60-80° C. adding it drop wise to 90-99% by weightof the said magnetic sensitive particles, mixing both with a laboratorykneader and allowing the coated particles, thus obtained in the form ofputty, to mature for about 24 hours at room temperature; (iv)synthesising magnetorheological fluid composition comprising the stepsof heating 10-20% by weight of the said carrier fluid as used in step(iii) to 60-80° C. in a container, adding 80-90% by weight of the saidcoated magnetic sensitive particles obtained from step (iii) to it,homogenising the mix thus obtained, in a high speed mixer and agitatingthe said mix followed by cooling it to the room temperature, furtheragitating the said mix and finally cooling the magnetorheological fluidcomposition, thus obtained, to room temperature.
 4. A process for thepreparation of magnetorheological fluid composition having castor oil asa carrier fluid and magnetic sensitive particles coated with themagnetic sensitive particles stabiliser dispersed in the said carrierfluid wherein the said magnetic particles stabiliser is synthesised fromthe same carrier fluid which is used to disperse the said coatedmagnetic sensitive particles.
 5. A magnetorheological fluid compositionas claimed in claim 2, wherein the said high purity iron particlescomprise carbonyl iron particles.
 6. A magnetorheological fluidcomposition as claimed in claim 2, wherein the said ferrite alloyincludes nickel zinc ferrite.
 7. A magnetorheological fluid compositionas claimed in claim 2, wherein the said ferrite alloy includes manganesezinc ferrite.
 8. A process for the preparation of magnetorheologicalfluid composition as claimed in claim 3, wherein the said high purityiron particles comprise carbonyl iron particles.
 9. A process for thepreparation of magnetorheological fluid composition as claimed in claim3, wherein the said ferrite alloy includes manganese zinc ferrite.
 10. Aprocess for the preparation of magnetorheological fluid composition asclaimed in claim 3, wherein the said ferrite alloy includes nickel zincferrite.